In the field of injection molding, U.S. Pat. No. 4,330,257 describes an injection molding machine that utilizes a fixed platen, a moveable platen, and an intermediate turret having four faces so that the faces are sequentially presented to the fixed platen as the turret rotates. The device includes mold halves and cores forming voids into which molten plastic is forced under pressure during a molding cycle. The turret carries cores on each of its faces, and complementary mold halves receiving the cores are attached to the fixed platen.
According to this patent, in operation, the movable platen forces the turret toward and against the cavity mold half carried by the fixed platen. Once a “shot” has been injected, the moveable platen and the turret are simultaneously drawn away from the fixed platen, and the turret is rotated through, e.g. 90 degrees, to present a new turret face to the fixed platen. The turret is moved away from the fixed platen by small hydraulic jacks 30, 33. The four positions of the turret, as it rotates through 90 degree arcs, may be termed positions 1, 2, 3 and 4, and the faces of the turret may be termed A, B, C, and D. Injection occurs at position 1. Ejection occurs at position 4. Initially, turret face A is at position 1. After injection of a first shot, the movable platen moves away from the turret and concurrently the turret moves away from the fixed platen to expose the molded articles carried by the core. The turret rotates through 90 degrees to bring another set of bare cores on turret face D into position 1, and the turret and movable platen then close and a second injection shot is performed. The turret and movable plate again move to their open positions and the turret is rotated through an additional 90 degrees. Now, turret face A is at position 3, with the cores extending into a hollow member 18 that enables the member to apply tonnage against the turret. The mold is closed again, and injection of a third shot occurs. The turret and movable plate again simultaneously move to their open positions and the turret is rotated through an additional 90 degrees. Now, turret face A is at position 4, and at this position, the molded articles are stripped from the cores as the mold closes again for a fourth shot. The mold is opened and the turret is again rotated through 90 degrees to bring the now bare cores on face A into registration with the cavities, and the process continues. After each injection, the mold remains closed and under pressure for a period. The mold is then opened and the turret is rotated. This system has the advantage of exposing the molded articles carried by the cores at positions 2 and 4, with ejection of the articles occurring at position 4.
The cost of producing a molded part depends upon a variety of factors. Of these, an important factor involves how rapidly parts can be produced, that is, how short can be the “cycle time”, that is, the time period between successive injection events. Methodology and equipment enabling cycle times to be reduced would contribute importantly to cost reductions in a molding operation.